Conventionally, there has been proposed an energy storage device in which stacked electrodes and terminals are joined to each other by clinch joining (see Japanese Patent No. 4374870, for example).
As shown in FIG. 20, the energy storage device includes: a stacked electrode 603 where a plurality of sheet sets each of which is formed of an insulation sheet 600, a positive electrode sheet 601, an insulation sheet 600 and a negative electrode sheet 602 are stacked, and the stacked electrode 603 has stacked layers 604 formed of an electrode foil projecting from a side of the insulation sheets 600; and a terminal 605 joined to the stacked layers 604 formed of an electrode foil.
The terminal 605 has plate portions 606, 607 in two layers, and the stacked layers 604 formed of an electrode foil are sandwiched between the plate portions 606, 607 in two layers of the terminal 605. By plastically deforming the plate portions 606, 607 in two layers, one plate portion 606 and the stacked layers 604 formed of an electrode foil are embedded into the other plate portion 607. With such a configuration, the stacked layers 604 formed of an electrode foil are joined to the terminal 605.
In the above-mentioned energy storage apparatus, a joined portion between the stacked layers 604 formed of an electrode foil and the terminal 605 is formed by contact joining using clinching. Accordingly, a surface of an electrode foil (portion having conductivity) is oxidized with a lapse of time, and electrical resistance of a joined portion between the stacked layers 604 formed of the electrode foil and the terminal 605 is increased. As a result, it becomes difficult to maintain electrical connection at the joined portion between the stacked electrode 603 and the terminal 605 in a favorable state.